Motors for automotive electrical equipment, such as door lock motors, generally have a female terminal structure so as to facilitate incorporation and electrical connection. FIG. 9 is a view showing the structure of a case lid of a conventional motor described in Patent Document 1. As shown in FIG. 9, the case lid includes a pair of female terminals to which externally inserted external terminals are connected. The female terminals are united with first ends of a pair of electrically conductive members, and first ends of brush arms are connected to second ends of the electrically conductive members. Brushes are joined to second ends of the brush arms. One of the paired electrically conductive members is cut at an intermediate position into two pieces, and a PTC element is sandwiched and held between the pieces. The electrically conductive members, which have resiliency, are assembled into grooves provided in the case lid formed of resin; and external terminals inserted from the outside are brought into contact with the female terminals provided at the first ends thereof. Thus, a structure for supplying electricity to the motor is formed. Further, by means of inserting a PTC element between the pieces of one electrically conductive member, the PTC element is connected in series to a circuit for supplying electricity to the motor so as to cut off excessively large current, to thereby protect the motor from burnout.
However, since external terminals are inserted directly into the case lid, the case lid must have holes which extend from the outer surface thereof into the interior of the motor. If a foreign object, grease, or the like enters the interior of the motor through the holes, the motor becomes unable to rotate. Furthermore, since the electrically conductive members are complicatedly routed within the case lid, the shape of the case lid becomes complex, and misalignment of a bearing is likely to occur because of sinking or deformation of the resin. Moreover, since the external terminals are inserted directly into the interior of the motor, if the external terminals are inserted erroneously, the external terminals shave a resin portion in the interior. In such a case, shavings of the resin may lock a rotor of the motor, or may hinder the supply of electricity, to thereby render the motor inoperable.
FIG. 10 is a view showing the configuration of a conventional motor described in Patent Document 2. Since the motor shown in FIG. 10 is of a type in which male terminals are used as power supply terminals, the motor does not have through holes extending into the interior of the motor. A PTC element is accommodated and held within a recess of a motor lid plate, which is fixed to a motor casing by use of a pair of pins. However, in the case of a miniature motor whose cylindrical cross section is small, a sufficiently large PTC element cannot be used. A small PTC element has a problem in that its high internal resistance lowers motor torque, its trip time is excessively short, and it becomes unable to perform continuous operation in a door-lock application or the like.
FIG. 11 is a view showing the interior of a case lid of a conventional motor described in Patent Document 3. The motor shown in FIG. 11 is configured such that a PTC element can be externally inserted into an opening portion of the case lid, whereby the PTC element can be assembled to the motor. This structure facilitates insertion and exchange of the PTC element. However, since the PTC element is exposed to the outside, the PTC element is apt to be mechanically damaged or receive influences of the ambient environment, whereby the function of the PTC element may be impaired. In particular, if the PTC element is contaminated by oil and trips, its internal resistance increases, which lowers the torque of the motor, and eventually makes the motor inoperable.
Patent Document 1: Japanese Utility-Model Application Laid-Open (kokai) No. H2-41663
Patent Document 2: Japanese Utility-Model Application Laid-Open (kokai) No. H2-41666
Patent Document 3: Japanese Utility-Model Application Laid-Open (kokai) No. H4-97456